Usually, a plurality of semiconductor IC elements are formed on a semiconductor wafer after the diffusion process and divided into individual semiconductor devices. The divided semiconductor devices are, for example, electrically connected to a lead frame using bonding wires and molded with resins, ceramics and the like to yield products.
With the scale down of the fabrication process and multifunctional designs of semiconductor IC elements advancing, the burn-in (screening) test has become indispensable for assuring the quality of products and for preventing troubles after packaging. The burn-in test, which involves applying temperature and electrical loads to semiconductor IC elements, has hitherto been carried out in the state of products. However, the mode of sales in which semiconductor IC elements are sold as separate devices (chips) has become widespread and the quality assurance in the wafer state has become important. Therefore, the burn-in test in the wafer state has also been carried out. In wafer level burn-in, defects ascribed to the process can be detected before assembling and the inspection time in a succeeding step can be shortened. In addition, the burn-in cost can be reduced. Therefore, an improvement in productivity and an inspection cost reduction can be achieved.
In order to carry out wafer level burn-in, it is necessary to apply electric power from a power supply together to electrodes (AL pads) necessary for the burn-in inspection of each of a plurality of semiconductor IC elements on a semiconductor wafer. This means that in the case of a large-diameter wafer of 300 mm, full contact with as many as 70,000 electrodes or more is necessary. For this reason, a probe card capable of full contact with a large number of electrodes on the wafer, i.e., a medium in which a large number of probe electrodes are arranged so as to be opposed to the many electrodes distributed on the whole wafer surface has been proposed and used. Refer to Japanese Patent Laid-Open No. 7-231019, for example.
Because a probe card is intended to come into simultaneous contact with the many electrodes distributed on the whole wafer surface as descried above, the probe electrodes are required to have very high positional accuracy. However, with the diameter of wafers becoming larger, it becomes more difficult than ever to pursue the positional accuracy of the probe electrodes. In order to improve the positional accuracy, there have been proposed methods that involve temporarily applying tension to the outside or inside of a contact sheet on which probe electrodes are formed and fixing this state by a separate rigid ring or correction jig, whereby prescribed positional accuracy can be obtained. Refer to Japanese Patent Laid-Open No. 2005-340485, for example.
A representative construction of a probe card is shown in FIG. 13. Reference numeral 31 denotes a semiconductor wafer, which has a plurality of pad electrodes (hereinafter referred to simply as electrodes) 32. A probe card 1 is constituted by a contact sheet 2, a localized anisotropic conducting rubber 3 and a glass substrate 4. The contact sheet 2 is such that on one surface thereof are formed bump electrodes 5 as probe electrodes for coming into simultaneous contact with the plurality of electrodes 32 on the semiconductor wafer 31 and on the rear surface thereof are formed isolated-pattern electrodes 6 so as to form pairs with each of the bump electrodes 5. These isolated-pattern electrodes 6 are connected to the electrodes of the glass substrate 4 via the localized anisotropic conducting rubber 3.
A method of manufacturing the contact sheet 2 is shown in FIG. 14. First, as shown in FIGS. 14A and 14B, a two-layer base material 10 formed from a Cu layer 8 and a polyimide layer 9 is stuck to a ceramics ring 7 having a small coefficient of thermal expansion. On that occasion, the two-layer base material 10 is caused to expand thermally by being heated to the order of 200° C., and is stuck to the ceramics ring 7.
Next, as shown in FIG. 14C, holes 11 for forming bumps are formed on the two-layer base material 10 by a laser, as shown in FIG. 14D, bump electrodes 5 are formed by coating growth at the locations of the holes 11, and as shown in FIG. 14E, the Cu layer 8 is removed with a prescribed size thereof left behind as isolated-pattern electrodes 6 (for details, refer to Japanese Patent Laid-Open No. 7-231019, for example).
FIG. 14F shows a completed contact sheet 2. In this contact sheet 2, the bump electrodes 5 and the isolated-pattern electrodes 6 (refer to FIG. 14E) are formed on the front and rear sides of the polyimide layer 9 (hereinafter referred to as the thin film sheet 9). The peripheral portion of the contact sheet 2 (the thin film sheet 9 with bumps) is fixed to the ceramics ring 7. The reason why the two layer base material 10 was caused to expand thermally in sticking thereof to the ceramics ring 7 in advance is that the thin film sheet 9 remaining after the removal of the Cu layer 8 (the coefficient of thermal expansion of Cu is 16 ppm/° C.) is caused to have a given tension so that looseness does not occur even when the temperature of the base material sheet 10 is raised to a burn-in temperature.
With the construction of the conventional probe card 1, however, when the two layer base material 10 is stuck to the ceramics ring 7 as described above, the ceramics ring 7 receives a large force inward due to the tension of Cu and the ceramics ring 7 contracts isotropically due to this force and simultaneously strains elliptically. The amount of strain generated on this occasion is as large as not less than 10 times the amount of contraction. Because the direction of strain is determined by small variations occurring when the ceramics ring 7 and the two-layer base material 10 are manufactured, it is very difficult to predict the direction of strain for the bump electrodes 5 of the two-layer base material. For this reason, it is substantially impossible to ensure accuracy above the variations in elliptical strain, which are difficult to predict, no matter how the accuracy of the hole 11 formed in the two-layer base material 10 is increased.
Local, small deviations occur also in the hole 11 itself due to the effect of the heat that the two-layer base material 10 receives from laser light, that is, due to the effect of the order of working, working time and the working environment. These deviations are also very difficult to control, and provide a factor responsible for impairing the positional accuracy of the bump electrode 5 formed for each hole 11.
In the method of Japanese Patent Laid-Open No. 2005-340485, as described above, a correction is made by temporarily applying tension to the outside or inside of the contact sheet 2. However, this method has problems including the problem that it is necessary to secure beforehand a region necessary for making corrections.